Combined Multichannel Intraluminal Impedance and pH Esophageal Testing Compared to pH Alone for Diagnosing Both Acid and Weakly Acidic Gastroesophageal Reflux

Background & Aims: Twenty-four-hour multichannel intraluminal impedance and pH (MII-pH) esophageal monitoring detects reflux episodes at all pH levels, including acid reflux and weakly acidic reflux (WAR). The aim of this study was to assess the accuracy of pH monitoring alone in detecting acid reflux and WAR compared with MII-pH. Methods: For the detection of acid reflux: 60 consecutive MII-pH studies of patients off acid suppression were included. All studies initially were read by exclusively analyzing pH tracing for acid reflux episodes. Subsequently, all studies were blindly read again analyzing MII-pH-detected acid reflux episodes (pH decrease of <4 and MII-detected reflux). For the detection of weakly acidic reflux 40 MII-pH studies were included. Each study initially was read by identifying WAR on the pH tracing. Subsequently, studies were re-analyzed using MII tracings, classifying MII-detected reflux episodes into acid, WAR, or nonacid reflux. Results: For the detection of acid reflux the pH alone compared with MII-pH yielded a specificity of 68%, 67%, and 58%, respectively, for either abnormal percentage time of pH less than 4, positive symptom index, or both. The percentage time that the pH was less than 4 was significantly higher using pH alone compared with MII-pH. Eighty-one percent of acid gastroesophageal reflux episodes exclusively detected by pH were associated with MII-detected swallow. For the detection of WAR compared with MII, pH alone had a sensitivity of only 28%. Eighty-three percent of WAR episodes detected by pH were not associated with MII-detected reflux. Conclusions: The use of pH alone for the detection of acid reflux is very sensitive but lacks specificity compared with MII-pH. pH alone may overdiagnose abnormal acid reflux in up to 22% of tested patients. Also, the use of pH for the detection of WAR has poor sensitivity.